Note: Descriptions are shown in the official language in which they were submitted.
~2~5
The object of the present :~lvention i5 a ~1~ or fluidifier ~or
steel slag.
The importc~nt -fuction o~ slag in steel ~orking and ~melting pro-
cesses is well kn~n: the slag~ reacting t~ h the molten me~al, absorbs
various impurities, as silicates7 ~ides~ sulphur~ phosphorous and
others.
The reaction between slag and molten metal is Yery important
for skeel production both in arc ~urnaces and in Martin Siemens furna-
ces and in o~ygen converters - wherein, over large quantities of ma-
teriil, a continuous and diffused contaot between the slag ~nd t~e
metal being smelted has to be produced and this is why the forming
of the slag is studied ~nth particular care.
For the process to start regularly~ it is first of all necessary
for the slag to be formed as rapidly as pvssible and ~ith the right
degree of ~iscosit~. This rapidity in the form m g o~ the slag is
far more felt in modern technique, where ~ne tends to accelerate to
the UtDtost all the stages o~ the steel ~-~orking process.
On ~he other hand, the slag is formed by introducing on the metal
bath lime or limestone~ ~ich talce a certain time to reach the molten
state and to start the slagging action. To shorten this melting time~
it is known to add to the lime and limestone some fluic~fying agents
or ~l~ces. As a general rule, the in~luence of the flu~ in the slag
lowers the de~sity of the same and the adhesion between steel and
slag, favouring the rise of the material to be eliminated.
A very rell known ~nd widespread fluid~^fier used nowadays is
essentially fluorite~ which ho~lever contains various imI*Irities~ as
for example silicates, silica and sulphur, ~hich produce delc~ys and
inconveniences in the production process~ ~loreover, the melting fluo-
rite normaIly causes the developmen~ of harm~ul gases, as silicon
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415
tetrafluoride .
I~ l~s also been proposed to use fl.uidifiers based on premixed
mixtures of -fluorite .~ith other naturll nnnerals, as dolomite, lime-
stone c~ld bau~ite, however essentially for economical reasons but
~ith no improvement of the teohnical characteristics of the actual
fluidifier.
The chemical composition of ~he slag :un ~ygen converters is
on the average the foIlo~ing:
CaO 30-41%
SiO22S~27%
~1203 2-3~
Fe oxides24~9%
MgO 5-~%
MnO ~ 47~
P205 1-1.5%
S 0~2-0~3~o
while, ;n arc fu m aces, the slag contains a smaller ~lantity of Fe
oxides. From the chemical point of view, it is fundamental for ~his
composition to keep a pre-established degree of basicity~ which is
normally expressed by the formula:
basicity index - (CaO ~ ~IgO)/(Si~2 ~ P205) = 3.5~3.7
~ le object of the present i~vention is to propose a new type
of flux for ste~l slag, belng apt to answer the aforespecified re-
quir~nents of basicity but allowin~, on the other hand~ to eliminate
the cited drawbacks of the l~nown fluidi~iers.
'~his result is obtained with the fluidifier according to the
yresent invention, which is essentially characterized m that it con-
sists of a synthetic mixture of c~lumInous and/or alum m a residues
with ~ne or more of th~ compcunds forming part of ~he group: clay,
-- 2 --
2~
marl (calcareous clay)~ sodil~l carb~late~ borclx (sodlum barate)~ ne~
pheline (s~lieate and orthosilicate of Al~ Na, ~, and ~entonite.
It should ~Imediately be poin~ed out that, by the t~rm ~alumi-
nous or ~lumina residues'l are meant scrap products coming ~rom the
production of alwminum, the aver~ge chemical an~l~sis of which is
the following:
70-90% al~nina (Al203)
~ -15% metallic alw mnum
10-12% mixtures of al~ninum hydroxide, of alumin~n trihydrate
and of calcium-aluminum silicates
The various constituents may enter the formation of the mixture
accordmg to the present invention in the following proportions:
fr~n 40 to 70% alum m ous and alumil~ residues
from lO to 20% clay
fron S to 10% borax
from 5 to 10~ sodi~ carbonate
from 10 to 20% marl
from S to 30% nephel~ne
~rom S to 10% bentoDite
Som0 examples of preferred compositions according to thc present
inv~ntion are given in the follo~nng table:
- ~ Oo--
I IIIII IV~
Aluminous and
alumina residues 70% 70% 66% 65%
Marl 10% 10% - -
Clay 10% - 109~ -
Sodiwn carb~nate 10% 1û% 10,'
Borax - S% - -
-- 3~
:~ZZ~
Nephe.line ~ 5% 7% 27%
Bentonite - - 7%
"----o 0~
The essential object of the aforedescribed ~lu~ mixtt~e i~ to
favouu and accelerate ~le fo~mation of reacti.ve slag with desulphu-
rizing and dephosphori~.ing qual:i~:ies~
An additional object of the present i~vention is however to also
favour a slag reducing reactîon. To this end, a ~urther object of
the present invention consists in the use vf sodium hydro~ide (Wa~l~
and of calcium carbide (Ca~2).
The addition of NaO~I to the flux is ho~ever not so simple~ as
the flu~ is thereby made highly hygroscopic and its storage3 in the
large quantities required for s~eelworks3 becomes extremely proble-
matic. On the other hand, also the addition of CaC2 is in turn very
delicate, since this produc~ ~y give rise~ with h~midity, to the
form m g of explosive mix~ures~
This problem is howe~er overcome, according to the present in-
vention~ by providing to mix 1 part of CaC2 with 1 or 2 parts of MaOH
and furthe~nore, preferably, ~ith 2 parts of sodium carbonate In
this way~ it has been possible to establish that the mi~ture - dried
and reduced into grains - is suf~iciently stableO A better result
is ob~ained by melting said mixture (taking advantage, for this pur-
pose, of the low meltir~ po m t of ~aO~I).
An eve~ fu~her stabili~y - anda above all, resistance to humi-
di.ty - is conferred by introducing in this mixture also 2 parts of
clay and 3 pQrts of limestone~
This reduc.ing mixture~ essentially based on NaO~I ~nd C~C2, is
introduced in ~he alUmin~lS ~1~LY according to the invention in the
proportion of from 2 to ~o3 according ts the type o~ steel produced~
-- 4 --
~ Ioreover it has been surp~isingl~ fo~nd ~ut that the addition
of alIsaline salts, specifically N~O~-I and/or sodiwn carbona*e to the
al~uNinous flu~, carries on a supplemen~ary function of puri~icationO
As a matter of fact a.luminous flux may easily contain ~npurities
which, reacting ~ith the cill~li.ne salts~ create compounds being after
~rard c~bsorbed in ~he lime slag of the furnace.
Such alkaline salts are added to the aluminous ~lux in a percen-
tage detern~ned ~ h respect to the cluantlty of ~he impurities in
the M ux, and in any case inferior to lO~. They may be added in
sol~tion state or in a dry state,
The flu~ mi~ture according to the present invention is prefera-
bly prepQred in pieces, grains or granules~ for example through pel-
leting te~miques Imo~rn per se. For thi.s purpose, binders can be
added to the mixture, in proportions varying between 0~3 and 2%~ con-
sisting for example of the known binding resins and hardeners normal-
ly eMpl~yed in the pelleting process, in the r~fracto~y mixtures and
in the mold~ng sands~ such as ~he silicone resins, ~he epoxy resins,
the silic~n-organic resins, polyethylene o~ide, ethylcellulose hydro-
xide~ and ~he like~ which volatilize at the melting temperature of
the steel and do no* affect, ~1erefore, ~he correct for~ing of the
slag.
Fur*hermore, ~he use of molasses as a binder has been found par-
tlcularly interesting. This product~ which may be utili~ed at the
pure state, o~ring to its intrinsic composition transforms itself -
at the high temperatures to which the flux is subjec~ed - leading
to the fonmation of nascent carbon7 this in t~n favours the redu-
cing reaction of the slag.
Considering tha* the modern metallurgical technique involves large
quantities of o~ygen ~both in ~ygen converters and in arc urnaces), the
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~ZZ41~
reducing feature of the flu~r, and h~nce of the slag, becomes hi~hly
important for reali~ing a cert~in neutrali~ation of the excess of oxygen
present in the actual Iw lten slag.
Finally, there iæ also the possibility to agglomerate ~he flux
miYture by making use of pitch~ in a ~a~ l~no~n per seO
The ~luidifier according to the present invelltion has been tested
in arc furnaces of 40, 60 ~nd 70 tons, in carbon steel castings, with
excellent results~ particularly for what concerns the prompt formation
of the slag. The t~sts have been carried out also m castings prepa-
red with different types of sLags~ c~lwc~ys 1rith excellent results.
An essenticilly positive side effect has reover been fo~ld in
a re~uction of the erosion effect of ~he furnace refractory lining
- at slag level - which can clearly be ascribed to the s.lightly basic
characteri~tics ~f the flux according to ~he inventîon~
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